Since an update a few weeks ago my Mint 11 desktop insists on displaying .jpg files from my /home/username directory , and those attached to emails, by opening LibreOffice3 instead of Image Viewer. And there is no longer a "do this from now on" option when specifically choosing some other display program.

If you have Ubuntu Tweak installed, I believe you can set/change the default .jpg viewer there.

Or you can do it manually by editing some files...(~/.local/share/applications/mimeapps.list and/or /usr/share/applications/defaults.list). Take a look at this guide, it doesn't refer to image files but it'll give you the general idea: http://www.libre-software.net/change-th ... int-ubuntu